Default answer: People are supposed to marry only within their
faith.
And if they must marry someone from a different religious tradition,
then one of them will convert to the religion of the other.

Creative answers: When designing a new relationship,
you are free to deal with religious matters any way you please.
But it is better to discuss religious affiliations,
rather than assuming that the less religious partner will convert.

How important is religion to each of you?
What religious practices do you follow?
What expectations does each of you have for the other concerning
religion?
For example, does one expect the other to convert to his or her
religion?
Will you seek a religious affiliation you can both agree on?
Will each of you keep your own religious practices and faith?

If you have children, what religion will the
children be?
Do you assume your children will 'naturally' be Jewish or Catholic?
Will your children be given any religious education? If so, what
kind?
Do your children already have some religious training
—especially if this is a second marriage or relationship?
How old must your children be to make their own religious decisions?
Will you force them to attend religious training until a certain age?

In some religions, the couple must promise to
raise the children
within the faith before the religious leader will marry them.
Are you aware of any such requirements? What will you do about
them?
Will either of you undergo religious re-training in preparation for
marriage?
Do you feel that you should be the same religion in order to be married.
(Or do the rules of one of your churches require you to profess that
faith
before you can be married in that church?)

People also have been known to change their
religious beliefs.
If one of you 'loses faith', how will that affect your relationship?
What will happen if one of you is converted to a new religion?

You might decide not to write any definite
answers to this Question,
but you should at least discuss the role of religion in your
relationship.
Will the religious expectations of relatives on either side have any
impact?